The present invention relates to the preparation of ion-exchange resin catalysts. More specifically, the invention relates to the preparation of partially-neutralized cation-exchange resins.
Ion-exchange resins frequently are employed as catalysts in the preparation of bisphenols from phenol and carbonyl compounds. For example, U.S. Pat. No. 3,394,089 teaches the use of a strong-acid cation-exchange resin partially neutralized with a C.sub.1 -C.sub.4 alkyl mercaptoamine such as 2-mercaptoethylamine (2-aminoethanethiol). Similarly, U.S. Pat. No. 3,760,006 teaches that the modification of an insoluble strong-acid cation-exchange in acid form by partial neutralization with a thiazolidine yields an improved catalyst for the preparation of bisphenols. The latter patent teaches that the thiazolidines easily may be prepared by the reaction of a ketone or aldehyde, H.sub.2 S, and an aziridine compound. In addition, it is known to prepare the mercaptoamines of the former patent from H.sub.2 S and an aziridine, such as ethyleneimine. See, e.g., U.S. Pat. No. 3,944,561 at column 2.
The partially neutralized ion-exchange resin catalysts are useful in the commercial production of bisphenols, especially bisphenol A. Unfortunately, current methods for producing the catalysts described hereinabove employ aziridine compounds which are somewhat hazardous. For example, ethyleneimine is described in The Condensed Chemical Dictionary (9th Edition) at page 361 as being highly toxic and corrosive; a dangerous fire and explosion hazard; and a known carcinogen. In view of these hazards, it would be very desirable to prepare said catalysts using a method which would not require the costly and hazardous aziridine compounds.